1. Field of the Invention
The present invention relates to a magnetic head and a tape-medium reading and writing apparatus that read magnetically recorded information by helical scanning.
2. Description of the Related Art
Recently, a sliding magnetic head having an MR (magnetoresistive) element has been developed as a magnetic reading head for use in digital video recorders and digital audio recorders. This magnetic head is used while being mounted on a rotary cylinder with a base plate therebetween in a state in which an MR element is inclined at a predetermined azimuth angle. The magnetic head reads magnetically recorded information using so-called helical scanning. That is, magnetically recorded information is read by rotating the rotary cylinder with the magnetic head in one direction while sliding a magnetic tape medium in the same direction.
Information is magnetically recorded in the form of digital signals with inductive heads with the narrow track width by so-called guard-bandless recording. That is, two to four inductive heads having different azimuth angles are mounted on a rotary cylinder, and are alternately brought into contact with a magnetic tape medium by the rotation of the rotary cylinder, thereby sequentially superimposing a track on a part of a track previously written on the magnetic tape medium.
In order to precisely read the tracks written by the above-described guard-bandless recording, the height from the base plate to the center in the track width of the MR element must be precisely fixed among the magnetic heads. For that purpose, a method has been adopted in which the MR element is positioned while observing a marker layer provided on a shielding layer under an optical microscope. An example of a marker layer is a convex portion provided on a shielding layer, as disclosed in FIG. 3 or 4 of Japanese Unexamined Patent Application Publication No. 2001-93120.
Helical scanning generally adopts a narrow write/wide read method in which the reading track width is larger than in a plate-shaped magnetic head, and the MR element has a track width that is almost double the written track width. For this reason, the reading characteristics of the MR element are required to be fixed at any position in the track width in order to reduce reading errors.
However, in the magnetic head disclosed in the above patent publication, the width of the convex portion is smaller than the track width of the MR element, and the height between the base plate and the MR element is substantially equal to the height of the convex portion. Therefore, both end portions of the convex portion in the direction of the track width of the MR element are placed within the track width. Because of such a convex portion, the asymmetry of the magnetic head (symmetry of the reproduced signal) substantially changes in the direction of the track width. Consequently, the reading characteristics cannot be fixed.